Engines may utilize recirculation of exhaust gas from the engine exhaust system to the engine intake system, a process referred to as Exhaust Gas Recirculation (EGR), to reduce regulated emissions and/or improve fuel economy. Additionally, engines may utilize turbochargers to increase power density and improve efficiency.
However, several issues related to over temperature conditions and under temperature conditions can arise with such systems, especially in a locomotive context using diesel engines. First, high EGR temperatures may require significant EGR cooling, such as where EGR heat is rejected to engine coolant. However, the locomotive engine duty cycle may result in excessive heat rejection to the engine coolant from the EGR, thereby requiring significantly increased engine cooling system size and performance criteria. Second, the expansion and associated temperature reduction of exhaust gasses through the turbine of a turbocharger can cause downstream emission control devices, such as catalytic converters, to cool below temperatures sufficient to perform a substantial amount of exhaust gas conversion (e.g. light-off temperatures). Light-off temperature may be defined as the temperature at which a catalytic converter achieves a predetermined conversion rate or efficiency. The cooled conditions can result in reduced conversion efficiency, thereby increasing regulated emissions.